This invention relates generally to an article and method for reinforcing and/or sealing hollow structures and structures including channels or spacing between surfaces, and more particularly to the use of expandable pre-formed plugs comprised of an expandable inner core and an outer skin which are suitable for reinforcing and/or sealing such structural members in a wide range of applications.
Recently, there has been an increase in the need for selective reinforcement, sealing, and resonance frequency alteration of hollow portions of various structural components. As referred to herein, the term xe2x80x9chollow portionsxe2x80x9d is meant to be expansive and additionally includes channels and spacing between surfaces. Pre-formed reinforcements that utilize expandable formulations, such as heat-activated polymeric foaming materials, have been developed for those purposes.
Although sealing and/or structural reinforcements comprised of heat-activated expandable foams are known in the industry, such conventional reinforcements typically consist of an expandable article comprised of a monolithic structure. Such single component formulations must often integrate two different, but important functions. First, the material must expand to fill a cavity or void. Second, the same material should durably adhere or bond to a portion of the structure being reinforced and/or sealed.
Because two or more important functional tasks are being addressed by a single formulation, the design of single component formulation expandable materials usually requires various compromises and material tradeoffs. For example, a certain ingredient of a single formulation homogeneous matrix might improve the expansion of the formulation, yet hamper the adhesion of the reinforcement to a given structure. Conversely, an ingredient that facilitates adhesion could impede the thermal expansion of the part. Moreover, in a significant number of applications, it is desirable for the reinforcement to function as a resonance frequency dampening device to reduce or eliminate vibration, in addition to acting as a sealant to impede the flow of water, air and/or vapors through a cavity. Consequently, monolithic materials often tend to impose design constraints.
The present invention recognizes the disadvantages and limitations often associated with monolithic constructions and provides an improved expandable, pre-formed plug comprised of at least two formulations. By constructing a pre-formed plug from two or more different formulations, each individual formulation can be better suited, or xe2x80x9cspecialized,xe2x80x9d to address or xe2x80x9ctargetxe2x80x9d different primary functions. Such specialization allows the present invention to provide an improved plug and method for reinforcement, sealing and/or dampening that can reduce some or eliminate all of the aforementioned concerns, while providing increased expansion, better adherence, improved corrosion resistance, and/or enhanced barrier, sealing, and/or dampening properties. The present invention provides the additional advantage of being efficient, generally cost-effective, and useful in connection with a large number of applications.
In accordance with one aspect of the present invention, an expandable pre-formed plug is provided that is suitable for sealing and/or structurally reinforcing a structure having surfaces defining a space therebetween (which may comprise the topography of an integrated structure). The plug includes an inner, expandable core having an outer surface and an outer skin that substantially encapsulates the core. More preferably, the plug includes a heat-activated inner core and an outer skin that is displaceable, and still more preferably, which substantially encapsulates the inner core. The pre-formed shape of the uncured plug may be of a generic size or shape or may be specifically designed to mate with the inner surface of a hollow portion of the structural member upon expansion. The outer skin is generally dry to the touch at room temperature. Upon application of a predetermined amount of heat, which generally initiates partial or complete curing, the core expands and the surrounding skin is displaced in a coordinated manner so the skin can contract and therefore durably adhere or bond to the walls of the structural member and the outer surface of the core. If necessary or desirable, the plug can further include one or more integrated or attached locating and attachment devices that can be used to temporarily locate or facilitate the orientation or placement of the plug in a given application.
In accordance with another aspect, the present invention provides a method for reinforcing and sealing a structure having surfaces defining a space therebetween. The method including the steps of: (i) providing a structure having surfaces defining a space therebetween; (ii) providing an expandable pre-formed plug having an inner, expandable core and a displaceable outer skin which substantially surrounds the core; (iii) inserting the plug into the space defined between two surfaces; and (iv) causing the plug to expand to cause the skin to bonding surface and therefore durably adhere or bond said surfaces.